I looked at the 393PC and Marinemax 382 last year. The 382 looked awfully small compared to the 393. I would advise the 393 with 4 people. Use the extra cabin for storing luggage, snorkel stuff whatever. The starboard side (I think) has the larger cabin so it would be equitable to have the second couple have access to both port cabins.

IMO, the more people you have on the boat, the harder it's going to be to keep everybody happy whether its shore excursions, bars or restaurants.

We had 4 of us on a 474 and it was great being able to have some private space.

An older boat sounds ok in theory, but we found that our 5 year old 474 "smelled" from the get go. This can be due to deteriorating toilet hoses or just plain old age. A stay with friends that owned a new cat really showed the difference (Hi Barb and Ron if you read this!) in how a boat smelled and looked and you will be living on it most of the time.

Maybe consider the newer 443 for 6 people as that would help with the costs.

Lastly, you could always rent a sailcat and just leave the sails down. However, there is far more room on the bridge of a powercat and the front deck is much more accessable for mooring as there is no sail rigging present there.